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David G. Clark and John W. Kelly

Rosa × hybrida `Meijikatar' plants were fertilized on weekdays with Hoagland's solution at 100, 200, or 300 mg·liter-1 nitrogen. Prior to simulated shipping, plants were treated with benzyladenine at 0, 25, 50, or 100 mg a.i.·liter-1. Plants were subsequently paper sleeved and stored in cardboard boxes in darkness at 16 C for 5 days.

On the day of harvest, plant height and number of flowers per plant were not affected by production nitrogen level. After removal from simulated shipping, total chlorophyll was increased in the lower leaves of plants grown at higher nitrogen rates and treated with higher rates of benzyladenine. Three and five days after removal from simulated shipping, the least percent leaf chlorosis was observed on plants treated with higher rates of cytokinin, but there was no effect of production nitrogen regime.

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Hermen Malik and Douglas D. Archbold

The potential for plant growth regulator (PGR) manipulation of `Chester Thornless' blackberry (fibus spp.) primocane growth was evaluated. PGR treatments included combinations of soil-applied uniconazole at 1, 5, 25, and 125 mg/plant and GA, foliar-applied one or two times at 100 ppm 3 and 4 weeks after a 25-mg/plant uniconazole application. Also, GA and BA were applied at 100 ppm alone or in combination one, two, or three times. Increasing rates of uniconazole reduced primocane length, leaflet count, and leaf, cane, and root dry weights. GA, applications reduced primocane length and increased branch elongation but failed to reverse the effects of uniconazole at 25 mg/plant, except those on branch length, leaflet count, and primocane dry weight. Only applications of BA + GA, increased both branch production and elongation and dry weights of some component tissues, while BA alone generally had no effects. Chemical names used: (E)-1-(p-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-1-penten-3-ol (uniconazole); N-(phenylmethyl)-1H-purin-6-amine (benzyladenine, BA); gibberellic acid (GA).

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Rongcai Yuan and Duane W. Greene

Experiments were conducted to evaluate the effects of BA, removal of bourse shoot tips including only folded leaves and growing point, and different numbers of leaves per fruit on fruit retention and fruit development in `More-Spur McIntosh'/Malling 7 (M.7) apple trees [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.]. Removal of the bourse shoot tip increased fruit retention, whereas BA thinned fruit regardless of whether shoot tips were removed or not. There was no interaction between BA application and shoot tipping. BA thinned fruit only when one leaf per fruit was on a girdled small fruiting branch, but not when leaf number per fruit was two or greater. Fruit weight and soluble solids concentration increased dramatically with increasing leaf number per fruit. BA reduced fruit growth rate when <16 leaves per fruit were present on the girdled branches between 3 and 7 days after treatment, but it did not affect fruit growth rate when 32 leaves per fruit were on the girdled branches. Increasing leaf number also increased viable seed number per fruit while decreasing the number of aborted seeds, but it had no effect on the number of total seeds per fruit. BA reduced the number of viable seeds per fruit only when the number of leaves per fruit was less than four. Results suggest that BA thins apple fruit mainly by reducing carbohydrates available to developing fruitlets. Chemical name used: N-(phenylmethyl)-1H-purine-6-amine [benzyladenine (BA)].

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V. E. Emongor and D. P. Murr

Benzyladenine (100 or 200 mg.litre-1) was applied to mature Empire/M.26 apple trees as dilute sprays 2, 4, 9, 11, 13, 15, 17, 20, 25, 27, 29 or 31 days after full bloom (DAFB). The most effective time of thinning was 25-29 DAFB (king fruit diameter 8.94-13.91 mm), and the thinning response to BA concentration was linear. Benzyladenine (BA) did not reduce fruit set when king fruit diameter was less than 5.35 mm, but BA significantly increased fruit weight, diameter (D), length (L) and L:D ratio compared to unsprayed controls and later BA treatments. BA - treated fruitlets had higher ethylene production, 24 hours and 7 days after spraying compared to untreated controls. We suggest that the response of apple fruitlets to BA applied as a thinner is mediated by ethylene. High fruit quality was obtained when BA was applied at 17-31 DAFB. Timing of BA sprays had no effect on seed number, though BA significantly increased seed number, fruit size, weight and L:D ratio. These results suggest that BA has the potential to substitute for the use of carbaryl as a thinner of apples in Ontario orchards.

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Duane W. Greene and Wesley R. Autio

Benzyladenine (BA) stimulated lateral branching on young apple (Malus domestica Borkh.) trees at concentrations as low as 100 mg·liter-1. BA reduced lateral shoot length indirectly through increased intersboot competition, whereas daminozide reduced lateral shoot growth as a direct effect of the chemical inhibition. Daminozide reduced the number of spurs that were induced by BA to grow into lateral shoots. BA reduced the size of terminal buds on spurs that were stimulated to grow into lateral shoots. When daminozide was included with BA, spur quality was increased, as determined by Increased bud size. The positive effect of daminozide on BA-treated spurs was indirect, and other growth retardants used in combination with BA may be equally effective at improving spur quality. It may not be possible to stimulate lateral branching with BA on young trees just coming into production without causing an unacceptable amount of thinning. However, on bearing `Empire' trees, lateral shoot growth was increased with BA while still achieving an appropriate level of thinning. In general, there was no advantage to applying BA in a split application. Chemical names used: N-(phenylmethyl)-1H-purine-6-amine [benzyladenine (BA)]; butanedioic acid mono(2,2-dimethylhydrazide) (daminozide).

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Richard H. White and Richard E. Schmidt

Field research was conducted to determine the effects of N, Fe, and benzyladenine (BA) on fall performance, post-dormancy recovery, and storage nonstructural carbohydrate composition of `Midiron' bermudagrass [Cy - nodon dactylon (L.) Pers.]. Fall green color retention and turf quality were superior for 48 than for 24 kg N/ha per month. Nitrogen level did not affect post-dormancy recovery or nonstructural carbohydrate levels in stolons and rhizomes measured in Sept. and Nov. 1983 and 1984. Iron level did not influence turf color and quality during summer months. Biweekly application of 0.6 kg Fe/ha produced better retention of greenness and turf quality during Fall 1983 and 1984 and superior turf color in Spring 1985 than the 0 kg Fe/ha treatment. Better green turf coverage was obtained with the biweekly than the monthly Fe (1.2 kg-ha-l) treatment during Fall 1983. In contrast, monthly Fe produced color and turf quality similar to that of the biweekly Fe treatment during Fall 1984. Nonstructural carbohydrates were similar among Fe levels in 1983 and 1984. The effects of Fe on turf color and quality were similar at each level of N and BA. BA level did not consistently influence turf color or quality and did not affect storage carbohydrate levels. When used in conjunction with moderate summer N fertilization, foliar-applied Fe can extend bermudagrass quality during fall without adversely affecting postdormancy recovery. Chemical name used: N- (phenylmethyl)-lH-purin-6-amine (benzyladenine, BA).

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Paul T. Wismer, J.T.A. Proctor and D.C. Elfving

Benzyladenine (BA), carbaryl (CB), daminozide (DM), and naphthaleneacetic acid (NAA) were applied postbloom as fruitlet thinning agents to mature `Empire' apple (Malus domestica Borkh.) trees. BA, NAA, and CB reduced fruit set and yield per tree, and increased fruit size, percent dry weight, soluble solidscontent and return bloom. Fruit size was reduced, return bloom, length: diameter ratio and flesh firmness were increased, and fruit set and yield unaltered by DM. Although fruit set and yield were similar for BA, NAA, and CB, BA treated fruit were larger, indicating that BA increased fruit size beyond the effect attributable to chemical thinning alone. BA increased the rate of cell layer formation in the fruit cortex, indicating that BA stimulated cortical cell division. NAA, CB and DM had no effect on cell division rate. Mean cortical cell diameter at harvest was increased by NAA and CB and reduced by DM. Cell diameter at harvest in BA-treated fruit was similar to the control. These data support the hypothesis that BA-induced fruit size increase in `Empire' apple results from greater numbers of cells in the fruit cortex, whereas the fruit size increase due to NAA or CB is a consequence of larger cell size. Chemical names used: N-(phenylmethyl)-1H-purine-6-amine [benzyladenine (BA)]; 1-napthaleneacetic acid (NM); 1-naphthalenyl methylcarbamate [carbaryl (CB)]; butanedioic acid mono (2,2dimethyl hydrazide) [daminozide (DM)].

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F.G. Dennis Jr.

In 1994, benzyladenine (BA, formulated as Accel, containing 1.8% BA and 0.18% GA4+7) was evaluated as an apple fruit-thinning agent. Naphthaleneacetic acid (NAA, 10 ppm) and carbaryl (60 g·liter–1) were also used, as well as combinations of these chemicals with BA. Whole trees were treated with either an airblast sprayer or a hand gun, BA being used at 15–20 g/acre. Good responses to BA were obtained in one of two trials, with both `Empire' and `Gala', but `Jonagold' and `Jonathan' were not responsive (one trial each). In general, response to NAA and carbaryl was more consistent. In only one orchard (`Gala') did BA appear to increase fruit size without reducing crop load. Combinations of BA with NAA or carbaryl were generally no more effective than one chemical alone, but such combinations overthinned in one experiment with `Empire'.

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Z. Y. Mao and D. W. Greene

Penetration of foliar-applied chemicals can be influenced by a number of environmental conditions including: light, temperature, and humidity. These change during the day. 14C-benzyladenine (BA) was applied to the upper or lower surface of McIntosh apple leaves from 6:0 0 to 21:OO hours at 3 hour intervals. The amount of BA entering a leaf over a 24-hour period was not influenced by the time of application. Temperature was correlated with BA retention in the wax layer (correlation coefficients, r=0.06 4 and r=0.70 for the upper and lower surfaces, respectively) and with penetration through the upper surface (r=0.58). BA penetration into the leaf was not correlated with light intensity, relative humidity, or time of droplet drying.

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Duane W. Greene and Wesley R. Autio

BA, NAA, and carbaryl at 75, 6, and 600 mg·liter-1, respectively, were applied alone or in combination to `Starkrimson Delicious' in 1989 and `Redspur Delicious' apples (Malus domestica Borkh.) in 1990. BA was effective alone, but when combined with carbaryl it thinned excessively. Thinning failed when BA was combined with NAA because many seedless pygmy fruit were formed and they persisted until harvest. BA and carbaryl were more effective than NAA at increasing return bloom. Return bloom was more closely related to total seed count than to final set. BA improved flesh firmness at harvest and after cold storage. None of the treatments influenced the development of calcium-related storage disorders following air storage. Chemical names used: benzyladenine (BA); naphthaleneacetic acid (NAA).